SCHLOCK IS A MISUNDERSTOOD art, especially in the hands of Mordecai Richler, Montreal novelist and author of the screenplay for the new film, Joshua Then and Now. After the following hatchet job, I daresay you'll agree.

Properly done, schlock conveys desperation by pointing out life's pitiful, somehow funny underpinnings. It works as self-satire in which the director knowingly winks at the audience--mocking yet still sympathetic to the foibles of his characters. Schlock should not be confused either with camp, where the actors are in on the spoof, or kitsch, which scores its levity precisely because everybody involved misses the joke.

Good schlock--like An American Werewolf in London or Risky Business--steps gingerly just this side of outright derision of its subjects. Bad schlock--St. Elmo's Fire--hates its characters intensely and usually ends up by offending us or making us squirm.

Now here is where Joshua Then and Now comes in. Richler's Joshua is the fact-based story of a poor Jewish writer growing up in Montreal who, by pluck and a marriage above his station, rises to most-envied-status to live among wealthy WASPs in the city's posh suburb of Westmount.

Comedy, social commentary--call it what you will--Joshua is mediocre schlock Schlockhas many relatives, easily understood by attaching a prefix to define precisely the derived form's relationship to the tradition. I cite several of the most exemplary: rock-schlock (Spinal Tap), cock-schlock (Porky's has this covered) and lock-schlock (prison classics like the oh-so-shameful The Longest Yard).

Because Joshua is so transparently hostile on the subject of religion and because it persists in taking itself too seriously, it must eternally be categorized as ethnic-schlock a brand tellingly dubbed shock-schlock With this variety, we are made, rather forced--for it is rammed down our throats--to feel the appalling "weirdness" of the ethnics in question.

With Joshua Shapiro our given ethnic is Jewish, persecution-complex and all. "Look how they eat?" we gasp as Josh egregiously woofs down a fancy plate at a posh WASP-establishment restaurant. "They do that?" we squeal as Joshua exhibits the dishonesty of Yer-Basic-Semite on the time-honored subject of money. Shock-shlock, no ands ifs or buts.

BUT JOSHUA'S DIFFICULTIES go way back. Richler bases his screenplay on his novel by the same name, something he did before more plausibly and palatably Apprenticeship of Duddy Kravitz. But the novel itself is not that good to begin with. Not Richler's best work, it is a provincial rendition of the self-hating Jewish man's odyssey, his archetypal pursuit of the elusive non-Jewish woman (subtley known as the shiksa).

Springing from the complicated relationship between pampered Jewish boy and his doting, suffocating mother, shiksa-ism sees the mama's boy hunting outside the tribe partly in spite and partly to assert his independence.

The trouble is, Richler can't make fun of the condition because he suffers from it. He harbors so much anger, presumably owing to his own mother, or to his own miserable upbringing in Montreal, that his novel gets bogged down by sheer malice. The fictional Joshua's mother is absurd--a vain, floozy stripper--and his coarse father (adequately played by Alan Arkin, in the film's only good performance) lives a cliche. Richler's story of Jewish lust/angst was better served by Philip Roth in Portnoy's Complaint.

So big deal, Richler wrote a bad book. His film, on the other hand, is a disaster. The man couldn't cut good screen dialogue with a Bowie knife and his facility with visual humor ends at the level of the dated "Expose Yourself to Art" poster. Clearly, Richler is treading in unfamiliar territory (he told a Toronto journalist he would be sticking to novels in the future). Joshua is a case of what experts call genre envy.

To be fair, though, blame for its demise should be spread among several conspirators. Director Ted Kotcheff greedily sought to corner Quebec's French-Canadian market (Joshua was made and expected to flourish in Montreal) by casting Gabrielle Lazure, a French-Canadian starlet, in the lead role of Joshua's whitebread bedmate. This idea backfired, however, because the real Lazure has a strong accent, immediately conspicuous to the Montreal ear. To patch this up, her lines have been dubbed by a monotoned off-screen actress whose voice doesn't at all sound like it comes from Lazure's body. Plainly, a huge fault, especially when the lip-sync falters in a key fight scene.

Second, Richler's onscreen "writer" (aren't they supposed to be sensitive?) is demolished by James (Once Upon a Time in America) Woods in a typically overheated ax murderer's job of acting. His nostrils perpetually flaring and his mannerisms obstinately childish even at "significant" moments (like the awful scene where his writer-pal dies), one thought sums Woods up: he gives great stereotypes. As Mr. Ackroyd would say: "The essence of ba-aa-ad cin-ee-ma."

As schlock-schlock goes, Joshuais a downer. But then, when it comes to trash, I'm a purist.